Abstract: Alumina doped with from 1 mole percent up to about 20 mole percent magnesia is suitable for use as a core material for casting and directional solidification of advanced super-alloys. The core material is leachable in KOH and NaOH in an autoclave at an elevated temperature and elevated pressure.

Abstract: A ceramic article suitable for use in the casting of advanced superalloy materials has a structure of a predetermined porosity content and consists of either 3Y.sub.2 O.sub.3 .multidot. 5Al.sub.2 O.sub.3, Y.sub.2 O.sub.3 .multidot. Al.sub.2 O.sub.3 or 2Y.sub.2 O.sub.3 .multidot. Al.sub.2 O.sub.3 or two-phase mixtures of these single-phase materials.

Abstract: A furnace for practising temperature gradient zone melting on one or more semiconductor bodies comprises a closable work chamber for receiving semiconductor bodies for processing, a radiant heat source which forms a first closure member and a heat sink which forms a second closure member, the closure members defining the work chamber and being mutually separable by, for example, a hydraulic actuator to allow access to the interior of the work chamber. A reflector is disposed between the heat source and heat sink in surrounding relationship to the semiconductor bodies being processed to ensure the maintenance of a uniform temperature gradient within the work chamber. The reflector and the heat sink are liquid cooled for the effective removal of heat therefrom. The heat sink is further provided with a plurality of radiation attenuating cavities to enhance the performance of the heat sink.